Technical Tip: FortiGate DHCP Server IP address show IP conflict or removed due to conflict

This article describes FortiGate DHCP Server IP address show IP conflict or removed due to conflict.

FortiGate is being used as a DHCP server & DHCP IP POOL addresses being used in Firewall IP POOL as well.

Do not repeat to use the same IP pool addresses for Firewall IP POOL addresses and DHCP IP POOL addresses.

When a Firewall IP pool is created and ARP reply is enabled, FortiGate will reply to ARP request packet to enable layer 2 communication. This ARP reply can cause IP conflict if the same pool of IP addresses are used by DHCP.

Example Configuration:

# config firewall ippool
    edit "testCWPIP"
        set startip 172.22.1.2
        set endip 172.22.1.125
        set comments "not working"
   next

# config system dhcp server
    edit 7
        set default-gateway 172.22.1.1
        set netmask 255.255.255.0
        set interface "port4"
# config ip-range
    edit 1
         set start-ip 172.22.1.2
        set end-ip 172.22.1.125
  next
end

FortiGate is still showing IP conflict after after going through the following articles:
Technical Tip: Resolving IP address conflicts when FortiGate is the DHCP Server

Related article:
Troubleshooting Tip: DHCP status 'Removed due to conflict'